1. Field of the Invention
The present invention generally relates to a detector system, e.g. for synchronization of an FEL (“Free Electron Laser”), and in particular to a combined, low-noise, self-compensating and nearly drift-free high-frequency phase detector circuit for continuous measurements, and especially to a self-calibrating, nearly drift-free phase detector module which is preferably, but not solely, applied in such a phase detector circuit.
2. Discussion of the Prior Art
The invention is based on the finding that conventional detector systems have a drift in the range of several picoseconds which is substantially caused by the temperature dependency thereof. For many applications, this value is too high and exceeds for instance significantly the value of 10-100 femtoseconds which is considered to be necessary for synchronization of the so-called XFEL (“X-Ray Free-Electron Laser”—a European X-ray laser project where electrons are first accelerated to high energies and then caused to emit high-intensity X-ray laser flashes). As the available low-drift detector systems often show considerable noise, they are unsuitable for the practical application in many cases.
Examples of known detector systems and circuits for minimization of drift and noise are e.g. shown in documents U.S. Pat. No. 3,883,755; U.S. Pat. No. 4,042,885; U.S. Pat. No. 4,155,050; U.S. Pat. No. 4,389,621; U.S. Pat. No. 4,728,884; U.S. Pat. No. 4,937,537; U.S. Pat. No. 5,210,509; U.S. Pat. No. 6,087,897; U.S. Pat. No. 6,167,242; U.S. Pat. No. 6,242,974; U.S. Pat. No. 6,340,903; U.S. Pat. No. 6,476,671; U.S. Pat. No. 6,781,450; U.S. Pat. No. 6,937,684; EP 0 540 052; EP 1 184 972; WO 99/36792; and WO 01/20350, however, none of these documents disclose solutions for the problems mentioned above.